The present invention relates to a motor, to a method of fabricating a motor and to a rotary apparatus utilizing the motor capable of providing excellent rotational accuracy and high durability.
Conventionally, in a rotary apparatus such as a rotary polygonal face mirror of a laser beam printer or HDD (hard disk drive), there is used a motor using dynamic pressure bearings.
In the conventional rotary body apparatus, a rotor member needs to rotate at a high speed and at a rate of several thousands through several ten thousands rotations/minute, and by using the dynamic pressure bearings, members on the side of a rotor are supported in noncontact relation during high speed rotation to thereby restrain wear of the members.
A motor shown by FIG. 7 is an example of a motor using such dynamic pressure bearings. The motor shown by FIG. 7 is provided with a base 110 fixed to a frame of a main body apparatus such as printer or HDD, a hub shaft 130 extended with a shaft 131 in a shape of a circular cylinder from the center of a hub 132 in a circular plate shape and a bearing ring 152 fixedly attached to an end portion of the shaft 131.
The base 110 is provided with a fitting portion 110a projected in a circular ring shape and a stator coil 140 is fixed to an outer peripheral face of the fitting portion 110a. 
A retaining ring 151 is fixed to a front end portion of the fitting portion 110a coaxially with the fitting portion.
The stator coil 140 comprises a sheet-like yoke 141 laminated with a single or a plurality of sheets having the same shape and coils 142 formed by winding lead wires at the yoke 141. The yoke 141 comprises a mounting portion in a circular ring shape and a plurality of winding portions extended from the mounting portion outwardly in the diameter direction and is fixed to the fitting portion 110a by inserting the fitting portion 110a into a hollow portion of the mounting portion. Coils 142 are formed by winding lead wires around the winding portions and a rotary magnetic field is formed by conducting electricity to the coils 142.
A circular ring portion 133 is extended from a peripheral edge portion of the hub 132 of the hub shaft 130 toward a lower direction and rotor magnets 160 are fixed to an inner peripheral wall of the circular ring portion 133.
A bearing ring 152 is coaxially fixed to the end portion of the shaft 131 of the hub shaft 130, the shaft 131 penetrates the retaining ring 151, the bearing ring 152 is rotatably arranged in the fitting portion 110a of the base 110 and the hub shaft 130 is rotatably supported by the base 110. Oil for lubrication is filled between the fitting portion 110a of the base 110 and the bearing ring 152.
Grooves for generating dynamic pressure are formed at an outer peripheral face and an upper and a lower end face of the bearing ring 152.
According to the motor of the conventional technology, the rotor magnets 160 fixed to the circular ring portion 133 of the hub shaft 130 are urged by the rotary magnetic field formed by the stator coil 140 and the hub shaft 130 is rotated. Further, in accordance with rotation of the hub shaft 130, the bearing ring 152 is rotated and the oil is drawn between the bearings ring 152 and the fitting portion 110a of the base 110 and between the bearing ring 152 and the retaining ring 151. Further, when the rotational number of the hub shaft 130 becomes equal to or larger than a predetermined rotational number, the bearing ring 152 is supported to float by the dynamic pressure.
The motor using such dynamic pressure bearings is provided with advantages in which wear among members is inconsiderable even in high speed rotation and excellent durability is achieved.
Now, according to the above-described motor, in the bearing ring 152, there is used a copper-series metal material and there is used a metal material of SUS for the base since the grooves for generating the dynamic pressure are easy to form and durability against wear to a degree of withstanding the use is provided. As other reason of using these materials, in a state in which temperature is elevated in rotating the motor, the linear expansion coefficient of the copper-series metal is larger than that of SUS, when a hollow portion of the inserting portion 110a of the base 110 is expanded, the bearing ring 152 is expanded more than the expansion of the hollow portion and a volume of a clearance between the fitting portion 110a and the bearing ring 152 is not varied considerably and accordingly, the generated dynamic pressure can be maintained constant regardless of temperature. Further, in the dynamic pressure bearing, it is necessary for generating predetermined dynamic pressure to maintain the clearance between the bearing ring 152 and the fitting portion 110a of the base 110 with accuracy of about xc2x11 micrometer.
Further, the bearing ring 152 is fixed to the shaft 131 of the hub shaft 130 by press fitting.
Further, the shaft 131 of the hub shaft 130 is formed in a circular cylinder shape since the shaft 131 is a rotary member and an inner vacant portion of the bearing ring 152 fixed to the shaft 131 is also formed in a circular cylinder shape. By influence of checking of a lathe, a section of either of an outer peripheral face of the shaft portion 131a and an inner peripheral face forming the inner vacant portion of the bearing ring 152, cannot be machined to a completely round shape (complete roundness) and actually, the section is machined to an irregular circle including the complete roundness.
When the shaft 131 having an outer peripheral face of the section in an irregular circular shape, is mounted to the inner vacant portion of the bering ring 152 similarly having an irregular circular section, the state in which all the faces are brought into contact with each other is not produced and in either of the circumferential direction and the axial direction, there is brought about a state in which contact portions and separated portions are irregularly arranged and there is produced portions where stress is concentrated in press fitting.
Further, a material which is easy to form the dynamic pressure generating grooves and having the large expansion coefficient, as mentioned above, is generally provided with low hardness and when the bearing ring 152 is formed by such a material and the bearing ring 152 is press-fitted to the shaft 132 of the hub shaft 130, the portions where stress is concentrated as mentioned above are liable to deform. When the bearing ring 152 is deformed in this way, it is difficult to generate and maintain the dynamic pressure having a predetermined magnitude, and therefore there poses a problem in which the rotational accuracy is deteriorated or there is a concern of wearing the bearing ring 152.
The present invention has been carried out in order to resolve the above-described problem and it is an object thereof to provide a motor capable of achieving excellent rotational accuracy and high durability, a method of fabricating the motor and a rotary apparatus utilizing the motor.
The present invention achieves the above-described object by providing a motor comprising a rotor member having a shaft portion, a bearing ring having an inner vacant portion, the inner portion being inserted with the shaft portion and fixed to the shaft portion, a supporting member having a hollow portion containing the bearing ring relatively rotatably, a plurality of electromagnets arranged to the supporting member coaxially and in a fixed state for generating a rotary magnetic field, rotor magnets fixed to the rotor member and urged by the rotary magnetic field generated by the electromagnets for rotating the rotor member and the bearing ring, and dynamic pressure generating means arranged at either of the bearing ring and the supporting member for generating dynamic pressure between either one of the bearing ring and the supporting member and other thereof, wherein at least one of an outer peripheral face portion of a fixing portion of the shaft portion to which the bearing ring of the shaft portion is fixed and an inner peripheral face of the bearing ring, includes contact portions projected linearly to other thereof and brought into contact with the other at three or more locations in a circumferential direction thereof and to separated portions are formed among the contact portions to separate and oppose with other portions.
According to the motor of the invention, at least either one of the inner peripheral face portion of the fixing portion of the shaft portion of the rotor member to which the bearing ring is fixed and the outer peripheral face portion of the bearing ring, is formed with the contact portions which are projected linearly and brought into contact with the other at the three or more locations in the circumferential direction.
The contact portions are formed by forming at least either one of the inner peripheral face portion of the fixing portion of the shaft portion of the rotor member to which the bearing ring is fixed and the outer peripheral face portion of the ring in a shape projected linearly at the three or more locations in the circumferential direction and inserting the shaft portion of the rotor member into the inner vacant portion of the bearing ring to thereby bring the contact portions into contact with an opposed member. When the contact portions are brought into contact with the opposed member in this way, the projected portions are pressed in accordance with the shape of the opposed member to widen toward unprojected portions to crush to deform in very small amounts, the machining error is corrected and the contact portions are formed by being brought into close contact with the opposed member with no clearance therebetween.
In this way, according to the invention, the contact portions are projected linearly and the separated portions are formed among the contact portions and accordingly, when the bearing ring is fixed to the shaft portion of the rotor member, the bearing ring or the shaft portion of the rotor member is pressed to the opposed member to deform into the shape in accordance with the opposed member thereby forming the contact portions. Further, the contact portions formed in this way are provided with the shape in accordance with the opposed member and are brought into close contact with the opposed member with certainty. Therefore, the contact portions of the shaft portion of the rotor member and the bearing ring can be controlled in accordance with positions of arranging the contact portions, stress by press fitting can be distributed with certainty at the contact potions, stress can be absorbed at the contact portions and deformation of the bearing ring can be avoided.
Further, the shaft portion of the rotor member and the bearing ring are brought into contact with each other linearly at the three or more locations in the circumferential direction and therefore, stress is distributed both in the circumferential direction and a length direction of the contact portions and deformation of the bearing ring can be avoided by effectively distributing stress.
It is necessary that the contact portions are arranged at the three or more locations. In the case of two locations stress supplied on the bearing ring is concentrated in a predetermined direction and the bearing ring is warped into an elliptical shape.
It is preferable that the contact portions are arranged at equal intervals in the circumferential direction at at least either one of the inner peripheral face portion of the bearing ring and the outer peripheral face portion of the shaft portion of the rotor member. The reason is that the bearing ring is brought into contact with the shaft portion of the rotor member by substantially uniform force with no deviation over the total in the circumferential direction, the stress is evenly distributed substantially uniformly over the total in the circumferential direction and deformation of the bearing ring can be avoided with certainty.
Further, it is preferable that the contact portions are arranged at the inner peripheral face portion of the bearing ring or the outer peripheral face portion of the fixing portion of the shaft portion over an entire length in the axial direction. Stress is distributed substantially uniformly over the total in the axial direction, thereby, deformation of the bearing ring can further be avoided.
Although the contact portions need to form linearly, the contact portions may be formed in a linear shape, a meandering shape or a curved shape. In this case, xe2x80x9clinearlyxe2x80x9d signifies that when the shaft portion of the rotor member is inserted into the bearing member, in the case in which the contact portions are pressed to the opposed member, the width of the contact portions becomes slender to a degree by which the contact portions are deformed by press force and are brought into close contact with the other. Accordingly, the contact portions include those in a slender strip shape having a width to some degree.
Further, the contact portion may be formed such that a distance between the contact portion and the other is smaller than that of the surrounding of the contact portion and the shape is restricted in view of a relationship with each other. Accordingly, at the outer peripheral face portion of the fixing portion of the shaft portion or the inner peripheral face portion of the bearing ring having the contact portions, the contact portions may not be necessarily formed to project outwardly more than the surroundings of the contact portions. For example, in the case in which the section in the radial direction of the inner peripheral face of the bearing ring is formed in an n-angular shape and the section in the radial direction of the outer peripheral face of the fixing portion of the shaft portion is formed in a circular shape, respective central portions in the radial direction of n of plane portions constituting the inner peripheral face of the bearing ring are disposed on planes the same as those in the surroundings, the central portions are formed to be more proximate to the outer peripheral face of the bearing ring than the surroundings to thereby constitute the contact portions and the plane portions from the central portions to corner portions on both sides constitutes the separated portions separated from the bearing ring.
According to the motor of the invention, the fixing portion of the shaft portion is formed in a shape of a circular cylinder, the inner vacant portion of the bearing ring is formed substantially in a shape of a polygonal cylinder coaxial with the bearing ring, the substantially central portions among corner portions of the inner peripheral face portion forming the inner vacant portion of the bearing ring can form the contact portions and the plane portions from the substantially central portions to the corner portions on the both sides can form the separated portions.
According to the motor of the invention, the fixing portion of the rotor member is formed in a shape of a circular cylinder, the bearing ring is provided with teeth-like portions projected inwardly over the axial direction at plural locations of three or more locations of the inner peripheral face portion forming the inner vacant portion, the teeth-like portions of the bearing ring can form the contact portions and the separated portions can be formed by other than the plural locations in the inner peripheral face portion.
According to the motor of the invention, the inner vacant portion of the bearing ring is formed in a shape of a circular cylinder, the fixedly attached portion of the shaft portion is formed substantially in a shape of a polygonal cylinder, edge portions thereof can form the contact portions and the plane portions among the edge portions can form the separated portions.
According to the motor of the invention, the inner vacant portion of the bearing ring is formed in a shape of a circular cylinder, the fixed attached portion of the shaft portion is provided with teeth-like portions projected outwardly over the axial direction at plural locations of the outer peripheral face portion, the teeth-like portions can form the contact portions and the separated portions can be formed by other than the plural locations in the outer peripheral face portion.
Further, the invention achieves the above-described object by providing a method of fabricating a motor comprising a bearing ring fixing step of fixing a bearing ring to a fixedly attached portion of a shaft portion in a state in which contact portions of the bearing ring are brought into contact with the fixedly attached portion of the shaft portion by press-fitting or shrinkage-fitting the fixedly attached portion of a rotor member having the shaft portion formed with the fixedly attached portion in a circular cylindrical shape having a diameter larger than a diameter of a circumference including free edge end portions of the contact portions to an inner vacant portion of the bearing ring having the contact portions projected inwardly and linearly from three or more locations in a circumferential direction of an inner peripheral face portion forming the inner vacant portion, an electromagnet fixing step of arranging a plurality of electromagnets to a supporting member to thereby form a rotary magnetic field coaxially with the supporting member having a hollow portion, a magnet fixing step of fixing rotor magnets to the rotor member so as to be urged by the rotary magnetic field formed by the electromagnets, and a bearing ring containing step of containing the bearing ring in the hollow portion of the supporting member.
The above-described motor according to the invention can be fabricated by the method of fabricating the motor.
Further, the invention achieves the above-described object by providing a method of fabricating a motor comprising a bearing ring fixing step of fixing a bearing ring to a fixedly attached portion of a shaft portion in a state in which contact portions of the shaft portion are brought into contact with an inner peripheral face portion of the bearing ring by press-fitting or shrinkage-fitting the fixedly attached portion of a rotor member having the shaft portion including the fixedly attached portion formed with the contact portions projected outwardly and linearly from three or more locations in a circumferential direction to an inner vacant portion of the bearing ring having the inner vacant portion in a circular cylinder shape having a diameter smaller than a diameter of a circumference including free edge end portions of the contact portions, an electromagnet fixing step of arranging a plurality of electromagnets to the supporting member in a fixed state so as to form a rotary magnetic field coaxial with the supporting member having a hollow portion, a magnet fixing step of fixing rotor magnets to the rotor member so as to be urged by the rotary magnetic field formed by the electromagnets, and a bearing ring containing step of containing the bearing ring in the hollow portion of the supporting member.
The above-described motor according to the invention can be fabricated by the method of fabricating the motor.
Further, the invention achieves the above-described object by providing a rotary apparatus having the motor according to the invention.